1. Field of the Invention
The present invention relates to a system with multiple refrigeration levels for the recovery of volatile organic compounds from process gas streams The system is driven by a thermal engine for the simultaneous production of refrigeration, useful process heat and inert gas.
2. Description of the Prior Art
It is well-known in the prior art to remove volatile organic compounds (VOCs) such as solvents from process gas streams such as may occur with the desorption of a solvent concentrating adsorber (typically activated carbon) or a closed-loop process oven. Such methods have not provided a practical facility for the separation of the removed solvents, particularly water miscible solvents from the steam condensed after the desorption process. Refrigeration systems, such as disclosed in U.S. Pat. No. 4,480,393 to Flink et al have not provided a method for recovering multiple solvents with different dew point temperatures. Similar disclosures are found in U.S. Pat. Nos. 4,332,092 to Hansotte; 4,262,430 to Janson et al and 4,150,494 to Rothchild. Moreover, such systems typically are energy inefficient. Such energy efficiency is contributed to, at least in part, by the use of multiple power supplies for various components of the system. For example, prior art systems utilize utility-supplied electrical energy for refrigeration, a separate combustion system for the purpose of supplying heat for the vaporization of VOCs, and a separate inert gas generating system.